The MRI apparatus is an apparatus that measures an NMR signal generated by atomic nucleus spin comprising tissue of an object, in particular human body and two-dimensionally or three-dimensionally images shapes and functions of the head, abdomen, extremities, and the like. In imaging, an object is disposed in a static magnetic field (a polarizing magnetic field B0), a high-frequency magnetic field pulse is applied together with a slice-selective gradient magnetic field pulse in order to selectively excite a certain region, and then a readout gradient magnetic field pulse is applied within the excitation range in order to perform phase or frequency encoding.
The readout gradient magnetic field pulse generates a magnetic field gradient in an arbitrary direction in order to generate a magnetic field intensity gradient in the static magnetic field space. Since the atomic nucleus spin performs precession at a frequency according to a gradient magnetic field intensity and the magnetic rotation ratio, an echo signal can be decomposed into a component of each frequency i.e., position by measuring an NMR signal (echo signal) in a state where a readout gradient magnetic field pulse was applied to perform frequency analysis represented by the Fourier transform. In the MRI apparatus, a group of encoded echo signals with a different phase or frequency is disposed in a measurement space (generally referred to as “k-space” and referred to as k-space hereinafter) before performing the two-dimensional or three-dimensional Fourier transform to reconstruct an image.
As a method for arranging echo signals, there is a radial sampling method in which echo signals are radially arranged around the origin of k-space while changing a rotation angle. In the radial sampling method, a group of measurement data acquired by sampling echo signals at respective angles is referred to as “Blade”. Since the blades at respective angles are intersected with each other and arranged in k-space in the radial sampling method, artifacts and uneven brightness are caused in case of an improper positional relationship between the blades, which results in image quality deterioration. The improper positional relationship is caused by shifting from a position in k-space specified by the echo signals in a pulse sequence due to various factors.
As a technique for correcting an error of the positional relationship between the blades, there is a technique for calculating a shift amount of echo signals in k-space from phase distribution of data in which the Fourier transform was performed for the echo signals of respective blades and reflecting the shift amount to k-space arrangement processing of the echo signals (for example, refer to Patent Literature 1). Also, there is a technique for calculating a shift amount in a phase encoding direction from a temporal change of peak positions of the echo signals in the phase encoding direction and using the shift amount for correcting the pulse sequence.